For packaging, storage, and transportation of bulk goods, box packages or other packages of rigid construction are used, which are placed on a base (usually a pallet). The box packages consist of boxes of corrugated board. A box of corrugated board is, as a rule, provided with an inner sack into which the bulk goods are placed. When filled with the bulk goods, such a package has a quadrangular shape, i.e., the shape of the paperboard box, and thus utilizes the transportation base maximally, even though the package as such is expensive.
Unit-load sacks are also used for packaging, storage, and transportation of bulk goods. A unit-load sack is less expensive than a box package, but its drawback is its round shape when filled, whereby it utilizes the transportation base less efficiently than a box package does. It is understood in the art that bulk goods do not have a specific shape in bulk, such as grains, fertilizers and other granular materials. Thus, unit-load sacks bulge when filled and do not retain any definite shape.
In prior art related to the invention, U.S. Pat. No. 3,670,880 (Burleson et al.) shows an arrangement wherein paperboard receptacles are filled with flexible products and then a stack of the paperboard receptacles is surrounded by a heat-shrinkable plastic outer covering. The paperboard receptacle is made of a multilayer corrugated board and protects the flexible products from moisture. More particularly, Burleson et al. shows a package construction including a receptacle having a flat bottom and sidewalls extending upward from the flat bottom. The flexible products are placed in the receptacle to extend over a top edge thereof. A closure is placed on the products and has downwardly extending peripheral sidewalls which overlap a portion of the sidewalls of the receptacle. The closure and the receptacle are made from multilayer corrugated board and in view of the overlap of the closure about the receptacle, the products are isolated from the ambient atmosphere. To seal the closure to the receptacle and thus the products within a housing of corrugated board, a plastic film outer layer is shrunk wrapped about the closure and the receptacle.
U.S. Pat. No. 5,005,335 (Yourgalite et al.) shows a stretch wrapping operation wherein there are two layers that are tightly wrapped around the articles through a banding process.
U.S. Pat. No. 4,968,951 (Everman et al.) shows a method in which an inner sack is formed from a reel of inner sack blanks, placed inside a paperboard box, filled when it is in the paperboard box and the both the inner sack and the paper board box are closed. By retaining the inner sack in the rigid paperboard box, the inner sack does not bulge upon its filling with the bulk goods.
Netherlands Patent No. 8900-271 describes a "large sack" or container which is typically prepared from woven material, e.g., polypropene fabric, and is provided with lifting loops at its corners to enable the container to be lifted vertically from its top. In this container, there are no discrete "inner" and "outer" packages but rather, there is but a single package which constitutes both the "inner" package in contact with the bulk goods in the interior and "outer" package which is exposed. Thus, this container is ready for use, i.e., it can be filled with bulk material and transported without additional components. The inner side of the package is provided with stiffening elements connecting adjacent sides, whereby when filled, the container obtains an essentially parallelepiped shape.
In view of the fact that the container of Netherlands '271 is lifted from its top, the material from which the container is made is required to be sufficiently strong to avoid collapsing upon the container being lifted in its intended manner. Thus, an appropriate safety factor of such a container would be 5:1 to 8:1. However, the requirement for a sufficient strength of the container limits the materials from which the container may be made. Specifically, the container should be made of a strong woven material in order to provide the necessary structural integrity and strength to enable the container to be lifted by means of the lifting loops. To make the container out of strong woven material, it is necessary to sew the seams of different pieces of woven material together to obtain the final form of the container. It is not possible to heat seal the seams together because heat sealing plastic fibers in the woven material, which are initially heat sealed and stretched to orient the molecules to provide strength, would cause the strengthening process to reverse itself and the woven material to lose its strength.